Method and apparatus for fast W-CDMA acquisition

ABSTRACT

Apparatus for classifying a ray is disclosed, wherein the ray is received at a code division multiple access receiver. The apparatus comprises: means for receiving a neighbouring cell list comprising at least information concerning scrambling codes used by, and timing information concerning at least one neighbouring cell; means for selecting a cell from the neighbouring cell list, the cell having associated therewith one or more scrambling codes; means for determining whether the number of cells in the neighbouring cell list exceeds a threshold; means responsive to a positive determination for attempting to classify the ray to the selected cell without utilising means for mixing a received signal with a scrambling code; and means responsive to a negative determination for mixing a received signal with a scrambling code used by the selected cell to provide a mixed signal, and for examining the mixed signal to determine if the ray originates from the cell.

This invention relates to apparatus for, and methods of, classifying aray received at a code division multiple access receiver.

The proposed universal mobile telephone system (UMTS) will use codedivision multiple access (CDMA) to communicate on both uplink anddownlink communications between node Bs and user equipment (UE).Downlink communications (node B to UE) will have a scrambling code,specific to the particular node B, modulated thereon. However, each slotof each frame (there will be fifteen slots in each frame) of downlinkcommunications is proposed to commence with a 256 chip universal word,which is not modulated with the scrambling code. This universal word isthe same for every slot of every frame, and its repeated transmission ishereafter referred to as the primary synchronisation channel (PSCH). UEscan detect node Bs, or cells, by detecting the PSCH without anyknowledge of the identity or location of the node B, its scrambling codeor its timing. However, all the information that can be gleaned from thePSCH is the slot timing. Frame timing, node B identity and scramblingcode information is not available from the PSCH channel.

It is proposed to transmit a secondary synchronisation channel (SSCH),on which a sequence of secondary synchronisation codes (SSCs) aretransmitted. The SSCs are transmitted for the first 256 chips of thefifteen slots in a frame. The sixteen different SSCs are constructedfrom position wise multiplication of a Hadamard sequence with a givensequence Z. The SSCs are orthogonal to the primary synchronisation code(PSC) and are almost orthogonal to the primary scrambling codes. Thereare 64 different SSC sequences proposed to be used in UMTS.

A UE will be able, for a ray corresponding to a signal received from acell, to detect the SSC sequences of a received signal corresponding tothe ray for fifteen consecutive slots, and from this determine thescrambling code group and the frame timing using a look-up table. Thereceived signal will then be correlated against each of eight scramblingcodes which form the scrambling code group, and the scrambling codeidentified by detecting a high degree of correlation from one of theresulting signals.

Determination of the scrambling code and frame and slot timing is knownas ray classification. This method of ray classification, hereaftertermed blind ray classification since it uses no knowledge of the cells,is slow since data must be accumulated over at least one frame. It alsorequires a relatively large amount of processor time, because thelook-up table is large, which is undesirable in terms of powerconsumption and in terms of maximising processor sharing flexibility.This method is repeated for each ray which is required to be classified,and is indicated schematically in FIG. 1. Referring to FIG. 1, themethod 100 comprises obtaining frame timing and code group informationat step 101, and obtaining the scrambling code at step 102. Steps 103and 104 cause steps 101 and 102 to be repeated for each unclassifiedray.

It is proposed for each cell to broadcast a neighbouring cell list on abroadcast channel (BCH). The neighbouring cell list will contain theidentity of the scrambling code and the approximate slot timing (towithin one slot) of each cell which is in the area surrounding the celltransmitting the BCH. Implicit in this information is the scramblingcode group. The BCH channel will have a low data rate and carry largeamounts of data, so the neighbouring cell list is not expected to berepeated very often, for example once every five seconds or so.

It is proposed at page 144 of “WCDMA for UMTS” by Antti Toskala andHarri Holma, ISBN 0 471 720518, to assist the blind ray classificationmethod using information concerning the relative timing between cells.

In accordance with a first aspect of the invention, there is providedapparatus for classifying a ray received at a code division multipleaccess receiver, the apparatus comprising:

-   -   means for receiving a neighbouring cell list comprising at least        information concerning scrambling codes used by, and timing        information concerning at least one neighbouring cell;    -   means for selecting a cell from the neighbouring cell list, the        cell having associated therewith one or more scrambling codes;    -   means for determining whether the number of cells in the        neighbouring cell list exceeds a threshold;    -   means responsive to a positive determination for attempting to        classify the ray to the selected cell without utilising means        for mixing a received signal with a scrambling code; and    -   means responsive to a negative determination for mixing a        received signal with a scrambling code used by the selected cell        to provide a mixed signal, and for examining the mixed signal to        determine if the ray originates from the cell.

In accordance with a second aspect of the invention, there is provided amethod of classifying a ray received at a code division multiple accessreceiver, the method comprising:

-   -   receiving a neighbouring cell list comprising at least        information concerning scrambling codes used by and timing        information concerning at least one neighbouring cell;    -   selecting a cell from the neighbouring cell list, the cell        having associated therewith one or more scrambling codes;    -   determining whether the number of cells in the neighbouring cell        list exceeds a threshold;    -   in response to a positive determination, attempting to classify        the ray to the selected cell using scrambling code group        information and without mixing a received signal with a        scrambling code; and    -   in response to a negative determination, mixing a received        signal with a scrambling code used by the selected cell to        provide a mixed signal, and examining the mixed signal to        determine if the ray originates from the cell.

According to a third aspect of the invention, there is provided a methodof classifying a ray received at a code division multiple accessreceiver, the method comprising:

-   -   (i) receiving a neighbouring cell list comprising at least        information concerning scrambling codes used by, and information        concerning the approximate slot timing of, at least one        neighbouring cell;    -   (ii) selecting a cell from the neighbouring cell list, the cell        having associated therewith one or more scrambling codes;    -   (iii) determining whether the number of cells in the        neighbouring cell list exceeds a predetermined threshold;    -   (iv) in response to a positive determination in step (iii),        attempting to classify the ray to the selected cell by (a)        identifying scrambling code group information associated with        the ray, (b) identifying scrambling code group information        associated with the selected cell, and (c) comparing the two        sets of scrambling code group information thereby to determine        whether the ray originated from the selected cell; and    -   (v) in response to a negative determination in step (iii),        mixing a received signal with a scrambling code used by the        selected cell to provide a mixed signal, and examining the mixed        signal to determine if the ray originates from the selected        cell.

There may be provided apparatus for classifying a ray received at a codedivision multiple access receiver, the apparatus comprising:

-   -   means for receiving a neighbouring cell list comprising at least        information concerning scrambling codes used by at least one        neighbouring cell;    -   means for selecting a scrambling code used by a given        neighbouring cell;    -   means for mixing a received signal with the selected scrambling        code to provide a mixed signal; and    -   means for examining the mixed signal to determine if the ray        originates from the given neighbouring cell.

There may be provided a method of classifying a ray received at a codedivision multiple access receiver, the method comprising:

-   -   receiving a neighbouring cell list comprising at least        information concerning scrambling codes used by at least one        neighbouring cell;    -   selecting a scrambling code used by a given neighbouring cell;    -   mixing a received signal with the selected scrambling code to        provide a mixed signal; and    -   examining the mixed signal to determine if the ray originates        from the given neighbouring cell.

There may be provided a method of classifying a ray received at a codedivision multiple access receiver, the method comprising:

-   -   determining if a timing characteristic of the ray falls within a        predetermined range of a timing characteristic of a ray        classified to a given cell;    -   in response to a positive determination, mixing a received        signal with a scrambling code used by the given cell to provide        a mixed signal; and    -   examining the mixed signal to determine if the ray originates        from the given cell.

There may be provided apparatus for classifying a ray received at a codedivision multiple access receiver, the apparatus comprising:

-   -   means for determining if a timing characteristic of the ray        falls within a predetermined range of a timing characteristic of        a ray classified to a given cell;    -   means responsive to a positive determination for mixing a        received signal with a scrambling code used by the given cell to        provide a mixed signal; and    -   means for examining the mixed signal to determine if the ray        originates from the given cell.

There may be provided apparatus for classifying a ray received at a codedivision multiple access receiver, the apparatus comprising:

-   -   means for receiving a neighbouring cell list comprising, for        each of a plurality of cells, at least timing information and        one of a) cell synchronisation code information, and b)        information from which cell synchronisation code information can        be derived;    -   means for deriving for at least one cell, if necessary, cell        synchronisation code information from the neighbouring cell        list;    -   a demodulator for demodulating a received synchronisation code        from the received ray;    -   means for determining a possible relative phase of a cell        synchronisation code, derived from the cell synchronisation code        information, for a given cell to the received synchronisation        code on the basis of the timing information;    -   a comparator for comparing at least part of the received        synchronisation code with at least a part of the cell        synchronisation code from the given cell at the relative phase;        and    -   means for determining, on the basis of an output of the        comparator, whether the received ray originates from the given        cell.

There may be provided a method of classifying a ray received at a codedivision multiple access receiver, the method comprising:

-   -   receiving a neighbouring cell list, comprising for each of a        plurality of cells at least timing information and one of a)        cell synchronisation code information, and b) information from        which cell synchronisation code information can be derived;    -   deriving for at least one cell, if necessary, cell        synchronisation code information from the neighbouring cell        list;    -   demodulating a received synchronisation code from the received        ray;    -   determining a possible relative phase of a cell synchronisation        code, derived from the cell synchronisation code information,        for a given cell to the received synchronisation code on the        basis of the tiling information;    -   comparing at least a part of the received synchronisation code        with at least a part of the cell synchronisation code for the        given cell at the relative phase;    -   determining, on the basis of the result of the comparison,        whether the received ray originates from the given cell.

Embodiments of the present invention will now be described, by way ofexample only; with reference to the accompanying drawings, of which:

FIGS. 1 is a flow chart illustrating a first, prior art, rayclassification method;

FIGS. 2, 3 and 4 are flow charts illustrating second, third and fourthray classification methods which are employed in the preferredembodiment of the invention; and

FIG. 5 is a flow chart illustrating a ray classification methodaccording to the invention.

Referring to FIG. 2, a second ray classification method 200 commenceswith step 201, which comprises obtaining the SSCH Hadamard codesequences received for a candidate ray in a conventional manner, i.e. bydemodulation of the received signal. In step 202, the neighbouring celllist received from a cell is examined, and the scrambling code group andslot time are obtained for a cell selected from that list. In step 203,the obtained sequence of SSCs corresponding to the ray is separatelycompared against the SSCs for the code group of the scrambling code ofthe selected cell at the central timing offset and at timing offsets oneslot either side of the central timing offset. If this does not resultin classification of the ray, steps 204 and 205 cause the procedure tobe repeated for a different cell. This is performed for each of thecells identified in the neighbouring cell list.

The second method 200 is substantially quicker than the blind rayclassification method described above with reference to FIG. 1. Once theSSC sequence has been determined, the blind classification searchrequires checking the sequence against 64 code groups at fifteendifferent frame timings, which amounts to 960 checks. Clearly, far fewerchecks are required for each cell in the neighbouring cell list usingthe second method 200. Also, since the number of cells against which asignal is checked is reduced, the second method 200 is more likely toresult in correct classification than the blind method.

In a modification of the second method 200, extra confidence in the cellclassification is provided. Here, a CPICH check is performed at step 204only when the SSCH search step 203 yields positive result, to confirmthat the scrambling code of the selected cell is the same as that usedto modulate the received signal. This CPICH check, put simply, involvescorrelating a received signal with the scrambling code used by theselected cell, and examining the result. The relative timing of the twosignals is set to isolate the unclassified ray using the detectedcommencement of PSCH bursts to identify the start of a slot, andaligning the scrambling code accordingly. Since CPICH channels carry aknown data sequence—it is currently anticipated to be all +1s—it is asimple matter to determine whether the scrambling code corresponding tothe selected cell is the same as and is synchronised with the scramblingcode on the received signal. Since the frame timing of the rayclassified to the selected cell is known, the correlation need only beperformed at one of the fifteen possible slot positions.

It will be appreciated that in this embodiment the sequence of SSCs isdetermined with reference to a look-up table, which relates SSCHsequences to scrambling code groups, from the identification of thescrambling code transmitted as part of the neighbouring cell list. In analternative embodiment (not shown) the neighbouring cell list includesthe sequence of SSCs, or information from which the sequence of SSCs maybe determined. Such information may be, for example, the identity of thescrambling code group or similar.

Referring now to FIG. 3, the third method 300 starts with step 301 byselecting the unclassified ray which has the highest power. Step 302then determines whether the unclassified ray has been checked againstall classified rays. On first performing the method, the answer to step302 necessarily is no, so step 303 selects one cell from which a ray hasbeen classified. It is a pre-condition of the third method 300 that atleast one ray has been classified, although the method performs betterthe larger the number of cells from which rays have been classified. Atstep 304, the rays classified to the selected cell are examined in turnto determine if one of the classified rays has a timing characteristicwhich falls within 80 chips of the selected unclassified ray. In thisembodiment, the timing of the start of PSCH bursts is used to determinethe relative timing of the unclassified ray and the classified rays,although other references could be used instead. 80 chips correspond to21 μs or 6.25 km. If there is a negative determination, the methodreturns to step 302. If it is determined in step 302 that theunclassified ray has not been checked against all classified rays, step303 selects a different cell for use by step 304. If step 304 yields apositive determination, step 305 performs a CPICH check using thescrambling code associated with the selected cell. This CPICH check, putsimply, involves correlating a received signal with the scrambling codeused by the selected cell, and examining the result. The relative timingof the two signals is set to isolate the unclassified ray using thedetected commencement of PSCH bursts to identify the start of a slot,and aligning the scrambling code accordingly. Since CPICH channels carrya known data sequence—it is currently anticipated to be all +1s—it is asimple matter to determine whether the scrambling code corresponding tothe selected cell is the same as and is synchronised with the scramblingcode on the received signal. Since the frame tiling of the rayclassified to the selected cell is known, the correlation need only beperformed at one of the fifteen possible slot positions. Step 306detects whether the CPICH check produced a positive result, and returnsto step 302 or advances to step 307 accordingly. The ray is classifiedaccording to scrambling code and frame timing at step 307, then step 308determines if there are any more unclassified rays. If there are moreunclassified rays, the third method 300 returns to step 301. Otherwise,the method ends.

When step 302 determines that an unclassified ray has been checkedagainst all classified rays, steps 309 and 310 are invoked to classifythe ray. Steps 309 and 310 constitute a blind ray classification, as isdescribed above with reference to FIG. 1, after which the ray isclassified in step 307.

The third method results in ray classification in a shorter time thanthe blind ray classification method described above, since with thethird method it is not necessary to decode the SSCH for fifteenconsecutive slots, which equates to 36,096 chips. Performing a CPICHcheck, on the other hand, can require only the first 512 chips of aslot. The third method also requires less processor time, since thecomplexity of an SSCH search and subsequent code group identification issignificantly higher than the complexity of a single CPICH check.Furthermore, since the CPICH channel is transmitted at a higher powerlevel than the PSCH and SSCH channels, the third method is more likelyto classify a ray to its cell than the blind ray classification methodor the second method described above.

Numerous variations on the third method 300 are possible. For example, asignal corresponding to a candidate ray could be checked against achannel other than the CPICH channel. The broadcast channel (BCH), forexample is suitable for this, since data modulated onto this channel ata low rate and the channel is modulated with a known OVSF code (OVSFcode number 1). CPICH checking is preferred since the CPICH channel isexpected to be transmitted at a higher power level than the BCH channel.Using the results from two channels, such as a BCH channel and a CPICHchannel, checked simultaneously or sequentially, provides an increasedprobability of ray classification if the ray does originate from thecell being checked against. The third method may be implemented inhardware, in software or in a combination of hardware and software.

Referring now to FIG. 4, the fourth method 400 starts with a number ofunclassified rays, arranged in descending order according to power, anda number of classified rays. A neighbouring cell list is decoded fromthe BCH channel received from a cell which the UE is listening to. It isnot necessary for the UE to be in communication with a node B, althoughthis is likely to be the case in practise.

The candidate ray having the highest power is selected, and a cell isthen selected from the neighbouring cell list in step 401. It is thendetermined whether or not one of the classified rays originates from thecell selected in step 402. If the answer is affirmative, step 403examines the relative timing of the strongest ray which has beenclassified to the selected cell to the candidate ray, and determineswhether the two rays are separated by more than 80 chips of thescrambling code, which equates to 21 μs or 6.25 km. In this embodiment,the timing of the start of PSCH bursts is used to determine the relativetiming of the unclassified ray to the classified ray, although otherreferences could be used instead. If the answer to step 403 isaffirmative, it is assumed that the candidate ray is not from theselected cell, and the method 400 proceeds to step 404.

If in step 402 it is determined that no rays from the selected cell havebeen classified, a CPICH check is performed on the candidate ray in step405 with the scrambling code being one slot earlier than the expectedtiming of the scrambling code. The CPICH check put simply involvescorrelating a received signal with the scrambling code used by theselected cell, and examining the result. The relative timing of the twosignals is set to isolate the unclassified ray using the detectedcommencement of PSCH bursts as the start of a slot, and aligning thescrambling code accordingly. Since CPICH channels carry a known datasequence—it is currently anticipated to be all +1s—it is a simple matterto determine whether the scrambling code corresponding to the selectedcell is the same as and is synchronised with the scrambling code on thereceived signal. If the result of step 405 is affirmative, i.e. thescrambling code and its timing is correct, then the candidate ray isclassified according to that code and that frame timing in step 406, andthe method 400 then proceeds to the end. If the result of step 405 isnegative, then a CPICH check is performed in step 407 with relativetiming equal to that expected. If in step 408 it is determined that thescrambling code and its timing is correct, then the candidate ray isclassified, and the method 400 proceeds to the end. Otherwise, a thirdCPICH check is performed in step 409 with the scrambling code delayedone slot compared to the expected timing of the scrambling code. If theresult is affirmative, the ray is classified accordingly in step 410,and the method proceeds to the end. Otherwise, it is determined in step404 if there are any more cells in the neighbouring cell list which havenot been tried for the candidate ray. If there are more cells, themethod is recommenced at step 401 where a new cell is selected from theneighbouring cell list. If there are no more cells, then the methodproceeds to the end, and the candidate ray requires classification byanother method if it is to be classified.

The fourth method results in ray classification in a shorter time thanthe blind ray classification method described above, since with thefourth method it is not necessary to decode the SSCH for fifteenconsecutive slots, which equates to 36,096 chips. Performing a CPICHcheck, on the other hand, can require only the first 512 chips of aslot. The fourth method also requires less processor time, since thecomplexity of an SSCH search and subsequent code group identification issignificantly higher than the complexity of a CPICH check. Furthermore,since the CPICH channel is transmitted at a higher power level than thePSCH and SSCH channels, the fourth method is more likely to classify aray to its cell than the blind ray classification method or the secondmethod described above.

Numerous variations on the fourth method 400 are possible. For example,a signal corresponding to a candidate ray could be checked against achannel other than the CPICH channel. The BCH channel, for example, issuitable for this since data modulated onto this channel at a low datarate and the channel is modulated with a known OVSF code (OVSF codenumber 1). CPICH checking is preferred since the CPICH channel isexpected to be transmitted at a higher power level than the BCH channel.Using the results from two channels, such as a BCH channel and a CPICHchannel, checked simultaneously or sequentially provides an increasedprobability of ray classification if the ray does originate from thecell being checked against. If it is not possible to identify thescrambling code used by a cell from the neighbouring cell list, themethod 400 may be required to be repeated using different scramblingcodes. If the neighbouring cell list does not contain timinginformation, then the method 400 may need to be modified to allow CPICHchecks at each of the fifteen possible relative timings. The fourthmethod may be implemented in hardware, in software or in a combinationof hardware and software.

FIG. 5 is a flow chart illustrating a ray classification methodaccording to the invention. Referring to FIG. 5, the method 500commence, then selects at step 501 the strongest unclassified ray. Onsubsequent runs, the step 501 comprises selecting the next strongestunclassified ray. At step 502, it is determined whether any rays have sofar been classified. If the answer is yes, then the method 500 proceedsto step 503. If the answer is no, which may occur for example onpower-up of a mobile telephone, step 504 causes a blind rayclassification check to be made on the ray. Blind ray classification isdescribed above with reference to FIG. 1. If the ray is not able to beclassified in this way, step 506 asks if there are any more unclassifiedrays, and returns to step 501 or ends the method 500 accordingly. If theray is classified, the classification data is stored at step 507 beforethe method proceeds to step 506.

At step 503, the attempt is made to classify the ray using steps 302,303, 304, 305 and 306 of the third method 300, described above withreference to FIG. 3. If in step 508 it is determined that the ray wasclassified by this, then the method 500 proceeds to step 507, where theclassification data is stored. Otherwise, the method 500 proceeds tostep 509.

At step 509, the method 500 detects the number of cells that appear in aneighbouring cell list which is received from a cell over a BCH channel.The number of neighbouring cells is compared to a threshold N, and themethod 500 proceeds to step 510 if the threshold is exceeded, orproceeds to step 511 otherwise. Step 510 comprises the second method200, described above with reference to FIG. 2. Step 511 comprises thefourth method 400 described above with reference to FIG. 4.

If the ray becomes classified by whichever of steps 510 and 511 wereimplemented, then step 512 causes the method 500 to pass to step 507,where the classification data is stored. Otherwise, the method passes tostep 504 where blind classification of the ray is attempted.

The value of the threshold N is hardwired into the apparatus whichimplements the method. This invention may be implemented in hardware,software or in a combination of hardware and software. The value of thethreshold is selected dependent on a number of factors including therequired speed of ray classification, processor speed and processoravailability. It will be appreciated that the fourth method 400 requiresless time to check a ray than the second method 200, unless there are alarge number of cells in the neighbouring cell list since less time isrequired to acquire the necessary data. Also, the amount of processingrequired to implement the fourth method 400 increases greatly as thenumber of cells in the neighbouring cell list increases, although thisis not true of the second method. In another embodiment, the value ofthe threshold is dynamically adjustable by a controller (not shown).

1. Apparatus for classifying a ray received at a code division multipleaccess receiver, the apparatus comprising: means for receiving aneighbouring cell list comprising at least information concerningscrambling codes used by, and timing information concerning at least oneneighbouring cell; means for selecting a cell from the neighbouring celllist, the cell having associated therewith one or more scrambling codes;means for determining whether the number of cells in the neighbouringcell list exceeds a threshold; means responsive to a positivedetermination for attempting to classify the ray to the selected cellwithout utilising means for mixing a received signal with a scramblingcode; and means responsive to a negative determination for mixing areceived signal with a scrambling code used by the selected cell toprovide a mixed signal, and for examining the mixed signal to determineif the ray originates from the cell.
 2. Apparatus according to claim 1,comprising means for initially detecting whether any classified raysexist; means responsive to a positive detection for determining if atiming characteristic of the unclassified ray falls within apredetermined range of a timing characteristic of the classified ray orone of the classified rays; means responsive to a positive determinationthereof for mixing a received signal with a scrambling code used by thecell to which the classified ray relates to provide a mixed signal, andfor examining the mixed signal to determine if the ray originates fromthat cell.
 3. A method of classifying a ray received at a code divisionmultiple access receiver, the method comprising: receiving aneighbouring cell list comprising at least information concerningscrambling codes used by and timing information concerning at least oneneighbouring cell; selecting a cell from the neighbouring cell list, thecell having associated therewith one or more scrambling codes;determining whether the number of cells in the neighbouring cell listexceeds a threshold; in response to a positive determination, attemptingto classify the ray to the selected cell using scrambling code groupinformation and without mixing a received signal with a scrambling code;and in response to a negative determination, mixing a received signalwith a scrambling code used by the selected cell to provide a mixedsignal, and examining the mixed signal to determine if the rayoriginates from the cell.
 4. A method according to claim 3, comprisinginitially detecting whether any classified rays exist, and, in responseto a positive detection, determining if a timing characteristic of theunclassified ray falls within a predetermined range of a timingcharacteristic of the classified ray or one of the classified rays; inresponse to a positive determination, mixing a received signal with ascrambling code used by the cell to which the classified ray relates toprovide a mixed signal; and examining the mixed signal to determine ifthe ray originates from that cell.
 5. A method of classifying a rayreceived at a code division multiple access receiver, the methodcomprising: (i) receiving a neighbouring cell list comprising at leastinformation concerning scrambling codes used by, and informationconcerning the approximate slot timing of, at least one neighbouringcell; (ii) selecting a cell from the neighbouring cell list, the cellhaving associated therewith one or more scrambling codes; (iii)determining whether the number of cells in the neighbouring cell listexceeds a predetermined threshold; (iv) in response to a positivedetermination in step (iii), attempting to classify the ray to theselected cell by (a) identifying scrambling code group informationassociated with the ray, (b) identifying scrambling code groupinformation associated with the selected cell, and (c) comparing the twosets of scrambling code group information thereby to determine whetherthe ray originated from the selected cell; and (v) in response to anegative determination in step (iii), mixing a received signal with ascrambling code used by the selected cell to provide a mixed signal, andexamining the mixed signal to determine if the ray originates from theselected cell.
 6. A method according to claim 5, wherein step (iv)(c)comprises comparing the two sets of scrambling code group information ata central timing offset indicated by the approximate slot timing of theselected cell.
 7. A method according to claim 6, wherein in the eventthat the ray is not classified to the selected cell, step (iv)(c)further comprises comparing the two sets of scrambling code groupinformation at a timing offset one slot before/after the central timingoffset.